28 FKAGMENTS OF SCIENCE. 



tion at a greater distance, and thus to determine the 

 law of its diminution. But how was he to find a body 

 at a sufficient distance? He had no balloon? and even 

 if he had, he knew that any height to which he could 

 attain would be too small to enable him to solve his 

 problem. What did he do? He fixed his thoughts 

 upon the moon; a body 240,000 miles, or sixty times 

 the earth's radius, from the earth's centre. He virtu- 

 ally weighed the moon, and found that weight to be 

 si^th of what it would be at the earth's surface. 

 This is exactly what his theory required. I will not 

 dwell here upon the pause of Newton after his first cal- 

 culations, or speak of his self-denial in withholding 

 them because they did not quite agree with the ob- 

 servations then at his command. Newton's action in 

 this matter is the normal action of the scientific mind. 

 If it were otherwise if scientific men were not accus- 

 tomed to demand verification if they were satisfied 

 with the imperfect while the perfect is attainable, their 

 science, instead of being, as it is, a fortress of adamant, 

 would be a house of clay, ill-fitted to bear the buffet- 

 ings of the theologic storms to which it is periodically 

 exposed. 



Thus we see that Newton, like Torricelli, first pon- 

 dered his facts, illuminated them with persistent 

 thought, and finally divined the character of the force 

 of gravitation. But, having thus travelled inward to 

 the principle, he reversed his steps, carried the prin- 

 ciple outwards, and justified it by demonstrating its 

 fitness to external nature. 



And here, in passing, I would notice a point which 

 is well worthy of attention. Kepler had deduced his 

 laws from observation. As far back as those observa- 

 tions extended, the planetary motions had obeyed these 

 laws; and neither Kepler nor Newton entertained a 



